Releasable subsurface apparatus for moving tools longitudinally in well bores



Sept. 17, 1957 M. B. CONRAD 2,805,533

RELEASABLE SUBSURFACE APPARATUS FOR MOVING TOOLS LONGITUDI-NALLY IN WELL BORES Filed. Nov. 21, 1955 I 2 Sheets-Sheet 1 Elll K l7;

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Sept. .17, 1957 M. B. CONRAD 2,806,538 RELEASABLE SUBSURFACE APPARATUS FOR MOVING y 5 TOOLS LONGITUDINALLY IN WELL BORES 195 2 Sheets-Sheet 2 Filed NOV. 21,

' INVENTOR. 4 .Maerwv B. 60/V/Ei0 RELEASABLE SUBSURFACE APPARATUS FOR MOVllgIG TOOLS LONGITUDINALLY IN WELL BORE Martin B. Conrad, Downey, Califl, assignor to Baker Gil fTools, Inc, Los Angeles, Calif., a corporation of Cati= ornia Application November 21, 1955, Serial No. 547,947

11 Claims. (Cl. 166-218) The present invention relates to subsurface well bore apparatus and more particularly to apparatus for moving other subsurface tools longitudinally in well bores.

An object of the present invention is to provide subsurface apparatus capable of lowering and elevating another well device in the well bore, theapparatus being readily and positively coupled to the well device in the well bore merely by moving the apparatus longitudinally of the device, and being hydraulically releasable from the well device merely by applying pressure to the fluid in the tubular string to which the apparatus is secured. Another object of the invention is to provide subsurface apparatus adapted to be run in a Well bore on a tubular string and coupled to another device in the well bore, the apparatus being hydraulically releasable from the device and providing a pressure indication to the operator at the top of the well bore when such release has occurred.

A further object of the invention is to provide a subsurface apparatus adapted to be coupled to and hydraulically released from another device in the well bore, the apparatus being relatively simple in structure and easy to operate.

This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration of a form in which it may be embodied. This form is shown in the drawings accompanying and forming part of the present specification. It will'now be described in detail, for the purpose of illustrating the general principles of the invention; but it is to be understood that Such detailed description is not to be taken in a limiting sense, since the scope of the invention is best defined by the appended claims.

Referring to the drawings:

Figure 1 is a side elevational and longitudinal sectional view of apparatus embodying the invention coupled to another device disposed in well casing;

Fig. 2 is an enlarged longitudinal section through the apparatus shown in Fig. 1, with parts being shown in relative position coupling the apparatus to the other device;

Fig. 3 is a cross-section taken along the line 3-3 on Fig. 2;

Fig. 4 is an enlarged cross-section taken along the line 44 in Fig. 1;

Fig. 5 is a view similar to Fig. 2, disclosing the apparatus being released from the other device;

Fig. 6 is a view similar to Fig. 2, disclosing the apparatus being connected to the other device.

The invention is illustrated in the drawings in association with a well packer A specifically designed to function as a bridge plug to be anchored in a well casing B in packed-0E condition against longitudinal movement in both an upward and a downward direction. The well packer is lowered in a well casing by a running-in tool C secured to the lower end of a tubular running-in string D extending to the top of the Well bore.

The specific well packer or bridge plug A disclosed, by itself, forms no part of the present invention, and is atet 'ice

specifically described in the joint application of Reuben C. Baker and Martin B. Conrad, for Well Packer Apparatus, Serial No. 425,646, filed April 26, 1954, now Patent No. 2,751,012. In that application the well packer is described as being run in the well casing B to the desired setting point merely by pushing it down the casing. During such pushing action, fluid in the well casing is capable of by-passing around the packer. Following its arrival at the desired location in the casing, the runningin string D can be released from the packer and pressure either from above or below the packer, as the case may be, is effective to anchor the packer to the well casing against downward or upward movement, the packer also being sealed against the casing to prevent leakage of fluid thereby. After the well packer has performed its function in the well casing, it can be retrieved by means of the running-in and retrieving tool C, or shifted by this tool'to another location in the well casing B. The well packer A can be pulled in an upward direction, if it is to be elevated to a new location in the casing; or it canbe pushed downwardly to a new location below its initial setting point.

In general, the well packer includes a tubular body 10 having a passage 11 therethrough that is valve controlled, as well as a control rod or bar 12 extending through the body to a substantial extent and terminating in an enlarged head 13 having a tapered upward guide end 14, as well as an upwardly facing tapered shoulder 15 at its lower portion. The head 13 may be threadedly secured to the remainder of the control rod 12, being held in such threaded position by a transverse pin 16.

Secured to the body 10 is an upwardly facing generally cup-shaped packing member 17 sealingly engaging the well casing, and also an upper expander 18 that tapers in a downward direction for cooperation with an upper set of circumferentially spaced strips 19 having friction drag portions 20 adapted to fri-ctionally engage the wall of the well casing B. The upper expander 18 and upper set of slips 19 coact with each other to anchor the well packer to the casing against downward movement therewithin.

Similarly, a set of circumferentially spaced lower slips 21 is disposed around the body 10 of the tool, having friction drag portions 22 for frictionally engaging the wall of the well casing, these slips being cooperable with a lower upwardly tapering expander 23 secured on the body. A downwardly facing lower packing cup 24 is also adapted to sealingly engage the well casing. The lower slips 21 and lower expander 23 coact with each to anchor the well packer to the casing against upward movement therewithin.

The upper and lower packing cups 17, 24 frictionally engage the wall of the Well casing, and since these packing cups are secured to the tubular packer body 10, the control rod 12 can be shifted longitudinally within the body 10 to determine the ability of the upper and lower expanders 18, 23 to anchor their respective slips 19, 21 against the wall of the well casing. In the event that the packing members provide insufiicient friction for obtaining the relative movement of the control rod 12, within the packer body 10, a friction drag device 25 maybe secured to the lower end of the body 10, this friction drag device frictionally engaging the wall of the well casing B.

Further details of the well packer A are unnecessary to an understanding of the present invention and may be found in the above-identified patent application. For purposes of the present description, it is sufiicient to point out that when the control rod 12 is disposed in a central and neutral longitudinal position Within the body It), to which position it'is normally urged by springs 26 engaging valve members 27 within the packer body, which are adapted to engage the rod 12 (of which only an upper valve head 27 is disclosed), pressure on the packer imposed from above can shift the upper packing member 17, packer body and upper expander 18 in a downward direction relative to the slips 19, to cause the upper expander to expand and hold the upper set of slips in anchoring engagement with' the well casing. With the control rod 12 in its neutral position, if pressure is exerted below the well packer, it will urge the lower packing cup 24, body 10 and lower expander 23 in an upward direction relative to the slips 21, the lower expander shifting the lower slips outwardly into anchoring engagement with the wall of the well casing, to prevent upward movement of the well packer within the casing. When in such neutral position, the control rod- 12- allows the upper and lower valves 27' (of which only the upper valve is disclosed in the drawings, there being; a lower valve in the packer body) to prevent flow of fluid in both longitudinal directions through the packer body passage 11.

As further explained in the above-identified patent application, the shiftingofthe control rod 12 in a downward direction relative to the packer body 10 will cause it to open the lower valve in the packer body, and allow fluid to bypass around the well packer by flowing through the packer body. At the same time, such downward shifting of the control rod within the body will serve the purpose of holding the slips 19, 21 in a central or neutral position with respect to the expanders 18, 23, preventing relative movement between the body and expanders with respect to the slips, in order to prevent the upper expander 18 from being wedged within the upper slips 19; Similarly, the control rod 12 can be shifted upwardly with respect to the body from its neutral or central position, to open the upper valve member 27 and allow fluid to by-pass through the bod-y passage 11, and around the well packer A. When in this upper position, the control rod 12 will again hold theslips 19, 21 in a central or neutral position with respect to the expanders 18, 23, and will prevent thelower expander 23 from moving upwardly with respect to the lower slips 21, to expand and anchor the latter outwardly against the wall of the-well casing.

As explained above, when the control rod 12 is allowed to occupy a neutral or central position within the body, then the body'10' and expanders 18, 23- can shift longitudinallywith respect tothe slips 19, 21-, longitudinal movement of the latter being resisted by the frictional engagement of' the drag block portions 20, 22 against thewall of the well casing. The. running-in and.retrieving tool C constitutes an apparatus for shifting the controlrod 1 2- downward within the body 10 when the well packer is being lowered in the well casing, to prevent the upper slips 19 from beinganchored against the casing. The running-in tool C can also be coupled or connected to the control rod 12 for the purpose of elevating the latter within the body 10 of' the tool A, to prevent the lower expander 23 from being wedged upwardly within the lower slips 21 and anchor the latter against the well casing. When the tool C is connected to the well packer A to shift the control rod 12 in the upward direction just described, the entire apparatus can be elevated in the well casing to a desired location in the latter, or may be removed completely from the well casing.

The running-in and retrieving tool C is connected to the lower end of the tubular running-in string D, which may consist of interconnected sections of tubing or drill pipe extending to the top of the well bore. The lower end of the running-in string is threadedly connected within the tubularhousing or cylinder 30 of the running-in and retrieving apparatus. This cylinder includes an'upperbody portion 31' threaded onto the lower end of the tubular-string D, andwhich has a relatively small diameter cylinder 32 therewithin. Below the small diameter cylinder portion of the housing is a larger diameter cylinder portion 33 interconnected to the small diameter cylinder portion by the intervening flange 34' integral with both portions. The lower end of the larger diameter cylinder portion 33 is threadedly secured to the upper end of a holding sleeve 35 having a lower internal tapered cam surface 36 that converges in a downward and inward direction. This cam or holding surface 36 terminates at an internal cylindrical surface 37, and the lower end of which merges into a downwardly diverging surface 38 coacting with the control rod head 13 to push the control rod 12 in a downward direction, as explained hereinbelow. The lower end of the holding sleeve 35 is threadedly secured to a sleeve extension 39 that may, in turn, be threaded onto a depending tubular guide 40 having a lower downwardly diverging tapered surface 41 for properly centering the entire running-in and retrieving apparatus C with respect to the control bar 12 when the former is to be disposed over the latter.

Slidably mounted within the housing 30 is the latch member 42 of the running-in and retrieving apparatus. This latch member is in the form of a tubular sleeve and includes an upper relatively small diameter piston 43 having suitable packing rings 44. thereon, slidably sealing against the wall of the small diameter cylinder 32. The latch member also includes alarger diameter piston portion 45 below the small diameter piston 43 carrying suitable piston packing 46 for slidablyseal'ing against the wall of the larger diameter cylinder 33. The two piston portions. 43, 45! are longitudinally spaced from each other, but are integral with one another. Depending from the larger piston 45 is a plurality of latch legs 47, which are disposed circumferentially completely around the. latch member and are separated from each other by relatively narrow slots 48, in order that they may be able to spring laterally in inward and outward directions. These legs 47 terminate in latch feet 49 that have external tapered surfaces 50 companion to the holding surface 36 of the sleeve 35, and also internal teeth 51 adapted to engage companion external teeth 52 formed on the control bar head 13.. These teeth 51, 52 are preferably constituted as V-shaped. threads formed: on. the latch feet and also on the; control. bar head, the latch. thread 51 tapering in both an upward and downward direction, in order to tend to cam. the latch feet 49 in an outward direction when they are moved longitudinally along the threads 52 of the control barhead13.

When the'latch sleeve 42 ismovedlongitudinally downwardof the housing 39, its latch feet 49 move relatively downward along the cam surface 36 and. are urged inwardly into coupling. engagement with the teeth or threads 52 of the. control bar head 13. When the latch feet have been coupled to. the control bar head, they can be retained in such. coupled. relation upon the taking ofan upward pull on the tubular string D, which will tend to shift: housing 30' upwardly, and thereby cause the. cam surface 36: to urge and hold the latch feet 49 in appropriate coupling engagement with the control bar head teethv 52. In the event the tubular string D andhousing 30 are moved in a downward direction, with the latch teeth. 51 in coupling engagement with the control bar head, such downwardmovement is limited by engagement of the diverging running-in surface 38 on the holding sleeve35 with the lower diverging surface 15 on the head. When these diverging surfaces are in engagement with each other, a lateral clearance space exists'between the tapered surfaces 50 onthe latch feet and the companion holding sleeve surface 49; to permit lateral outward movement of the latch feet and disengagement of their threads 51 from the control bar or rod head thread 52;, in the manner explained, hereinbel'ow.

In the event it is desired to unscrew. the latch teeth 51 from the control bar head 13, as. a result of rotating the. tubular string D and: housing 30, the rotary movement. of the. housing. is'transmitted to. the latch feet. 49 through a lateral or radial pin53 securedto the: housing; as throughuse of welding. material: 54, and extending inwardly between adjacent latch feet. The threads 51', 52 are preferably made left-hand, in order that right-hand rotation of the tubular string D and housing 30 will effect rotation of the latch feet and the entire latch member 42 in a right-hand direction, the latch feet 49 unthreading relatively in an upward direction from the control rod head 13, thereby effecting a disconnection between these members.

The latch member 42 is normally urged in a downward direction within its confining housing 30 by a helical compression spring 55 circling the upper portion of the latch member, with its upper end bearing against the housing or cylinder flange 34, and its lower end bearing against the larger piston 45. The latch member 42 is movable in an upward direction within the housing 3! by providing hydraulic pressure in the liquid contained within the tubular string D and the running-in apparatus C itself. The mere pumping of fluid at the proper rate down the tubular string D and through the hollow piston 43, 45 will build up a back pressure on the underside of the large piston 45, tending to elevate the latch member 42, since the spaces between the latch feet 49 are relatively small and will effectively provide a throttling action to the downward flow of fluid through said spaces, the lower portion of the head 13 being provided with appropriate longitudinal slots 56 to permit fluid to flow between the head 13 and the lower portion of the holding sleeve 35.

When fluid is being pumped at the proper rate through the apparatus, the back pressure built up will be exerted in an upward direction over the annular area of the large piston 45, tending to shift it in an upward direction. Such pressure will also be exerted in a downward direction over the annular area of the small piston 43, but inasmuch as the area of the large piston is much greater than that of the small piston there will be a resultant differential area facing in a downward direction over which the fluid pressure is acting, tending to elevate the latch member 42 against the force of the spring 55. Any liquid in the cylinder space 57 between and externally of the pistons can pass to the exterior of the housing through one or more bleeder holes 58 provided in the housing adjacent the housing flange 34.

The running-in and retrieving apparatus C can be used for lowering the well packer A, or corresponding tool in the well bore or well casing B. It is merely slipped over the control head 1-3 and the control bar 12 depending therefrom, the latch feet 49 ratcheting over the head thread 52 until the diverging holding sleeve surface 38 engages the lower diverging head surface 15. Thereafter, any downward movement of the tubular string D is transmitted through the housing 30 to the control bar 12 directly through the diverging surfaces 38, 15, shifting the control bar 12 to a downward position, which will hold the slips 19, 21 in their neutral position with respect to the expanders 18, 23, as well as holding the lower valve (not shown) in the body open. The apparatus can then be moved down the well casing B to the location at which the well packer is to be set.

In order to release the running-in apparatus C from the control bar 12, fluid is pumped down the tubular string and through the pistons 43, 45 into the housing 30, the fluid actin in an upward direction on the large piston 45 lifting the latch member 42 and the latch feet 49 relative to the threads 52 on the control head 13. At this time, there is sufficient lateral clearance between the tapered surfaces 56 on the latch feet and the holding sleeve cam surface 36 to permit lateral outward movement of the feet, to disengage their threads 51 from the control head threads 52. As the latch member 42 moves upwardly, the latch feet will merely ratchet over the head threads 52, until the latch feet have been completely disengaged from the threads 52, which effects an uncoupling between the running-in tool C and the control head 13. The tubular string D may now be elevated to elevate the running-in and retrieving apparatus C above the control head 13, whereupon the packer springs 26 6 will center the control bar 12 and allow the pressure in the well casing B, imposed either above orbelow the well packer A, to anchor the tool against downward or upward movement, as the case may be.

In the event it is desired to retrieve the well packer A, it is merely necessary to lower the running-in string D and the apparatus C, the guide 40 passing over the head 13, the apparatus being lowered until the diverging surfaces 15, 38 again coengage. The latch feet 49 will ratchet in a downward direction over the head teeth 52, being disposed opposite or in coupling relation to such teeth when the diverging surfaces 15, 38 engage. Thereafter, upward movement of the tubular string D will elevate the housing 30, to move the cam surface 36 upwardly relative to the latch feet 49, which action will urge the latch teeth 51 inwardly and hold'them coupled to the control bar head 13 (Fig. 2). Continued upward movement of the tubular string vD and housing 30 will now carry the control bar or rod 12 upwardly with it, the control bar being shifted within the body 10 of the tool A to its upper position, which will then place the slips 19, 21 in a neutral location relative to the expanders 18, 23, allowing the apparatus to be elevated in the well casing D, and to be completely removed from the well bore, if desired.

The large diameter cylinder 33 has an area which may be represented by the letter S, whereas the small diameter cylinder 32 has an area that may be represented by the letter R. Accordingly, the fluid under pressure used to hydraulically release the latch member 42 from the control bar head 13 is acting in an upward direction on the lower piston 45 over the resultant area S minus R, which area can be made quite substantiah'to insure the proper elevation of the latch member 42 against the compressive force of the spring 55, in order to release the latch feet teeth 45? from the control bar head 13.

It is, accordingly, apparent that the retrieving tool C can be coupled to the control bar head 13 merely by a downward movement of the apparatus relative to the control bar, as represented in Fig. 6. The running-in and retrieving tool C and the well packer A therebelow are then movable downwardly merely by lowering the tubular string D, the retrieving and running-in apparatus C and the well packer A. Similarly, the entire combination of apparatus can be elevated in the well casing B, merely by elevating the tubular string D, the control bar 12 remaining positively coupled to the running-in string by virtue of the camrning and holding action of the cam surface 36 against the latch feet 49, maintaining them in full threaded engagement with the threads 52 on the control bar head 13 (Fig. 2).

Whenever it is desired to release the running-in and retrieving apparatus C from the well packer A, it is merely necessary to pump fluid at the proper rate down through the tubular string and the apparatus, a back pressure being built up within the housing 30 for action on the underside of the larger piston 45 over the area S minus R, which will shift the latch member 42 in an upward direction, and cause the latch feet to ratchet freely over the head member threads 52 to a fully disengaged position, whereupon the tubular string D and the runningin and retrieving apparatus C can be raised above the well packer A and its control bar 12 (Fig. 5).

If difficulty is encountered in hydraulically releasing the latch feet 49 from the control bar head 13, then-the tubular string D need merely be rotated to the right, which will effect rotation of the housing 30, pin 53 and latch member 42 relative to the control bar head 13, causing the feet 49 to unscrew completely from the control bar head 13, whereupon the tubular string D and the running-in and retrieving tool C can be elevated in the well casing B free from connection to the control bar 12 and the well packer A therebelow.

The inventor claims:

1. In apparatus to be releasably coupled to a device in a well bore: a member adapted to be connected to a tubular string to be lowered in the well bore and to be disposed over the device; latch means carried by and movable longitudinally of said member and adapted to be coupled to the device; said member having a surface thereon engaged by said latch means when said latch means moves longitudinally of said member in one direction to hold said latch means in a laterally inward position coupled to the device; said member having a first cylinder and a second cylinder of greater diameter than said first cylinder; a first piston and a second piston connected to said latch means and slidable in said first cylinder and said second cylinder, respecively; said pistons being subject to the pressure of fluid in the tubular string to shift said latch means longitudinally of said member in the opposite direction to a position uncoupled from the device.

2. In apparatus to be releasably coupled to a device in a well bore: a member adapted to be connected to a tubular string to be lowered in the Well bore and to be disposed over the device; latch means carried by and movable longitudinally of said member and adapted to be coupled to the device; said member having a surface thereon engaged by said latch means when said latch means moves relatively downward of said member to hold said latch means in a laterally inward position coupled to the device; said member having an upper cylinder and a lower cylinder of greater diameter than said upper cylinder; an upper. piston and a lower piston connected to said latch means and slidable in said upper cylinder and said lower cylinder, respectively; said pistons being subject to the pressure of fluid in the tubular member to elevate said latch means in said member to a position uncoupled from the device.

3. In apparatus to be releasably coupled to a device in a Well bore, the device having an external thread: a member adapted to be connected to a tubular string to be lowered in the well bore and to be disposed over the device; latch means carried by and movable longitudinally of said member and having an internal thread companion to and adapted to be releasably coupled to the external thread of the device; said member having a surface thereon engaged by said latch means when said latch means moves longitudinally of said member in one direction to hold said latch. means in a lateral inward position with its internal thread coupled to the external thread of the device; and means for transmitting rotary motion of said member to said latch means to unthread said latch means from the device.

4. In apparatus to be releasably coupled to a device in a Well bore, the device having an external thread: a member adapted to be connected to a tubular string to be lowered in the well bore and to be disposed over the device; latch means carried by and movable longitudinally of said member and having an internal thread companion to and adapted to be releasably coupled to the external thread of the device; said member having a surface thereon engaged by said latch means when said latch means moves longitudinally of said member in one direction to hold said latch means in a lateral inward position with its internal thread coupled to the external thread of the device; means for transmitting rotary motion of said member to said latch means to unthread said latch means from the device; said member having a first cylinder and a second cylinder of greater diameter than said first cylinder; a first piston and a second piston connected to said latch means and slidable in said first cylinder and second cylinder, respectively; said pistons being subject to the pressure of fluid in the tubular string to shift said latch means longitudinally of said member in the opposite direction to a position uncoupled from the device.

5. In apparatus to be releasably coupled to a device in a well bore, the device having an external thread: a member adapted to be connected to a tubular string to be lowered in the well bore and to be disposed over the device; latch means carried by and movable longitudinally of said member and having an internal thread companion to and adapted to be releasably coupled to the external thread of the device; said member having a surface thereon engaged by said latch means when said latch means moves longitudinally of said member in one direction to hold said latch means in a lateral inward position with its internal thread coupled to the external thread of the device; means for transmitting rotary motion of said member to said latch means to unthread said latch means from the device; and hydraulic means responsive to fluid pressure in the tubular string for moving said latch means longitudinally of said member in the opposite direction to a position uncoupled from the device.

6. In apparatus to be releasably coupled to a device in a well bore, the device having an external thread: a member adapted to be connected to a tubular string to be lowered in the well bore and to be disposed over the device; latch means carried by and movable longitudinally of said member and having an internal thread companion to and adapted to be releasably coupled to the external thread of the device; said member having a surface thereon engaged by said latch means when said latch means moves relatively downwardly of said member to hold said latch means in a lateral inward position with its internal thread coupled to the external thread of the device; means for transmitting rotary motion of said member to said latch means to unthread said latch means from said device; said member having an upper cylinder and a lower cylinder of greater diameter than said upper cylinder; an upper piston and a lower piston connected to said latch means and slidable in said upper cylinder and lower cylinder, respectively, said pistons being subjcct to the pressure of fluid in the tubular string to shift said latch means upwardly of said member to a position uncoupled from the device.

7. In apparatus to bereleasably coupled to a device in a well bore: a member adapted to be connected to a tubular string to be lowered in the well bore and to be disposed over the device; latch means carried by said memher and adapted to be coupled to the device; spring means acting between said member and latch means for moving said latch means longitudinally of said member in one direction; said member having a surface thereon engaged by said latch means when said latch means moves longitudinally in said one direction to hold said latch means in a laterally inward position coupled to the device; said member having a first cylinder and a second cylinder of greater diameter than said first cylinder; a first piston and a second piston connected to said latch means and slidable in said first cylinder and second cylinder, respec tively', said piston being subject to the pressure of fluid in the tubular string to shift said latch means longitudinally of said member in the opposite direction to a position uncoupled from the device.

8. In apparatus to be releasably coupled to a device in a well bore, the device having an external thread: a member adapted to be connected to a tubular string to be lowered in the well here and to be disposed over the device; said member having an upper cylinder and a lower cylinder of greater diameter than said upper cylinder; a tubular latch structure movable longitudinally of said member, said structure including an upper piston and a lower piston slidable in said upper cylinder and lower cylinder, respectively, said structure further including latch legs depending from said lower piston and having an internal thread companion to and adapted to be releasably coupled to the external thread of the device; said member having a surface thereon engageable by said depending legs when said latch structure moves longitudinally of said member in one direction to hold said legs ina lateral inward position with their internal threads coupled to the external thread of the device; said pistons being subject to the pressure of fluid in the tubular string 9 to elevate said latch structure in said member to uncouple said depending legs from the device.

9. In apparatus to be releasably coupled to a device in a well bore, the device having an external thread: a member adapted to be connected to a tubular string to be lowered in the well bore and to be disposed over the device; said member having an upper cylinder and a lower cylinder of greater diameter than said upper cylinder; a tubular latch structure movable longitudinally of said member, said structure including an upper piston and a lower piston slidable in said upper cylinder and lower cylinder, respectively, said structure further including latch legs depending from said lower piston and having an internal thread companion to and adapted to be releasably coupled to the external thread of the device; said member having a surface thereon engageable by said depending legs when said latch structure moves Ion. gitu'dinally of said member in one direction to hold said legs in a lateral inward position with their internal threads coupled to the external thread of the device; said pistons being subject to the pressure of fluid in the tubular string to elevate said latch structure in said member to uncouple said depending legs from the device; and means for transmitting rotary motion of said member to said latch structure to unthread said latch legs from the device.

10. In apparatus to be releasably coupled to a device in a well bore, the device having an external thread: a member adapted to be connected to a tubular string to be lowered in the well bore and to be disposed over the device, said member having an upper cylinder and a lower cylinder of greater diameter than said upper cylinder; a latch structure carried by said member and including an upper piston and a lower piston slidable in said upper cylinder and said lower cylinder, respectively; said latch struucture having legs depending from said lower piston, said legs having an internal thread companion to and adapted to be releasably coupled to the external thread of the device; spring means acting between said latch structure and member urging said latch structure downwar-dly of said member; said member having a surface thereon engaged by said legs when said latch structure moves downwardly of said member to hold said legs in a lateral inward position with their internal threads coupled to the external threads of the device; said pistons being subject to the pressure of fluid in the tubular string to elevate said latch structure in said member to a position uncoupling said internal threads from said external threads.

11. An apparatus to be releasably coupled to a device in a well bore, the device having an external thread: a member adapted to be connected to a tubular string to be lowered in the well bore and to be disposed over the device, said member having an upper cylinder and a lower cylinder of greater diameter than said upper cylinder; a latch structure carried by said member and including an upper piston and a lower piston slidable in said upper cylinde-r and said lower cylinder, respectively; said latch structure having legs depending from said lower piston, said legs having an internal thread companion to and adapted to be releasably coupled to the external thread of the device; spring means acting between said latch structure and member urging said latch structure downwardly of said member, said member having a surface thereon engaged by said legs when said latch structure moves downwardly of said member to hold said legs in a lateral inward position with their internal threads coupled to the external threads of the device; said pistons being subject to the pressure of fluid in the tubular string to elevate said latch structure in said member to a position uncoupling said internal threads from said external threads; and means for transmitting rotary motion of said member to said latch structure to unthread said latch legs from the device.

References Cited in the file of this patent UNITED STATES PATENTS 2,232,949 Jones et a1 Feb. 25, 1941 

